The trachea begins immediately below the larynx (voicebox) and runs down the center of the front part of the neck ends behind the upper part of the sternum. Here it divides to form two branches that enter the lung cavities. The trachea, or windpipe, forms the trunk of an upside-down tree and is made up of fibrous and elastic tissues and smooth muscle with about twenty rings of cartilage, so that themycontentbreak head and neck may twist and bend during the process of breathing. The lining includes cells that secrete mucus along with other cells that bear very small hair like fringes. This mucus traps tiny particles of debris, and the beating of the fringes moves the mucus up and out of the respiratory tract, keeping the lungs and air passages free.